Exaggerated Error Handling Hurts! An In-Depth Study and Context-Aware Detection

Operating system (OS) kernels frequently encounter various errors due to invalid internal states or external inputs. To ensure the security and reliability of OS kernels, developers propose a diverse set of mechanisms to conservatively capture and handle potential errors. Existing research has thus primarily focused on the completeness and adequacy of error handling to not miss the attention. However, we find that handling an error with an over-severe level (e.g., unnecessarily terminating the execution) instead hurts the security and reliability. In this case, the error-handling consequences are even worse than the error it attempts to resolve. We call such a case Exaggerated Error Handling (EEH). The security impacts of EEH bugs vary, including denial-of-service, data losses, broken control-flow integrity, memory leaks, etc. Despite its significance, detecting EEH remains an unexplored topic. In this paper, we first conduct an in-depth study on EEH. Based on the findings of the study, we then propose an approach, EeCatch, to detect EEH bugs in a context-aware manner. EeCatch accurately identifies errors and extracts their contexts (both spatial and temporal), and automatically infers the appropriate severity level for error handling. Using the inferred severity level, EeCatch finally detects EEH bugs in which the used error handling exceeds the inferred severity level. By analyzing the whole Linux kernel, EeCatch reports hundreds of potential EEH bugs that may cause security issues such as crashing the system. After evaluating 104 cases reported by EeCatch, we manually confirmed 64 EEH bugs and submitted patches for all of them. Using our patches, Linux maintainers have fixed 48 reported EEH bugs, confirming the effectiveness of EeCatch. To the best of our knowledge, we are the first to systematically study and detect EEH bugs. We hope the findings could raise the awareness of the critical consequences of EEH bugs to help developers avoid them.